‘Rogue’ asteroids may be the norm

February 3, 2014

Artist rendering of the triple system : Romulus, Sylvia, and Remus (credit: European Southern Observatory)

A new map of asteroids developed by researchers from MIT and the Paris Observatory charts the size, composition, and location of more than 100,000 asteroids throughout the solar system, and shows that rogue asteroids are more common than previously thought.

Particularly in the solar system’s main asteroid belt — between Mars and Jupiter — the researchers found a compositionally diverse mix of asteroids.

The new asteroid map suggests that the early solar system may have undergone dramatic changes before the planets assumed their current alignment. For instance, Jupiter may have drifted closer to the sun, dragging with it a host of asteroids that originally formed in the colder edges of the solar system, before moving back out to its current position. Jupiter’s migration may have simultaneously knocked around more close-in asteroids, scattering them outward.

“It’s like Jupiter bowled a strike through the asteroid belt,” says Francesca DeMeo, who did much of the mapping as a postdoc in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “Everything that was there moves, so you have this melting pot of material coming from all over the solar system.”

DeMeo says the new map will help theorists flesh out such theories of how the solar system evolved early in its history. She and Benoit Carry of the Paris Observatory have published details of the map in Nature.

To create a comprehensive asteroid map, the researchers first analyzed data from the Sloan Digital Sky Survey, which uses a large telescope in New Mexico to take in spectral images of hundreds of thousands of galaxies. Included in the survey is data from more than 100,000 asteroids in the solar system.

DeMeo grouped these asteroids by size, location, and composition. She defined this last category by asteroids’ origins — whether in a warmer or colder environment — a characteristic that can be determined by whether an asteroid’s surface is more reflective at redder or bluer wavelengths.

The team then had to account for any observational biases. While the survey includes more than 100,000 asteroids, these are the brightest such objects in the sky. Asteroids that are smaller and less reflective are much harder to pick out, meaning that an asteroid map based on observations may unintentionally leave out an entire population of asteroids.

To avoid any bias in their mapping, the researchers determined that the survey most likely includes every asteroid down to a diameter of five kilometers. At this size limit, they were able to produce an accurate picture of the asteroid belt. The researchers grouped the asteroids by size and composition, and mapped them into distinct regions of the solar system where the asteroids were observed.

As the team writes in its paper, “the trickle of asteroids discovered in unexpected locations has turned into a river. We now see that all asteroid types exist in every region of the main belt.”

A shifting solar system

The compositional diversity seen in this new asteroid map may add weight to a theory of planetary migration called the Grand Tack model. This model lays out a scenario in which Jupiter, within the first few million years of the solar system’s creation, migrated as close to the sun as Mars is today. During its migration, Jupiter may have moved right through the asteroid belt, scattering its contents and repopulating it with asteroids from both the inner and outer solar system before moving back out to its current position — a picture that is very different from the traditional, static view of a solar system that formed and stayed essentially in place for the past 4.5 billion years.

“That [theory] has been completely turned on its head,” DeMeo says. “Today we think the absolute opposite: Everything’s been moved around a lot and the solar system has been very dynamic.”

Clark Chapman, a senior research scientist at the Southwest Research Institute in Boulder, Colo., says the new map is a welcome update to the asteroid maps he and his colleagues developed in the 1980s, which included only those asteroids measuring 20 kilometers or more in diameter. In the past two decades, he says, scientists have made leaps in their understanding of asteroids’ dynamics and evolutionary history, which DeMeo and Carry have now put into context.

DeMeo adds that the early pinballing of asteroids around the solar system may have had big impacts — literally — on Earth. For instance, colder asteroids that formed further out likely contained ice. When they were brought closer in by planetary migrations, they may have collided with Earth, leaving remnants of ice that eventually melted into water.

“The story of what the asteroid belt is telling us also relates to how Earth developed water, and how it stayed in this Goldilocks region of habitability today,” DeMeo says.

Abstract of Nature paper

Advances in the discovery and characterization of asteroids over the past decade have revealed an unanticipated underlying structure that points to a dramatic early history of the inner Solar System. The asteroids in the main asteroid belt have been discovered to be more compositionally diverse with size and distance from the Sun than had previously been known. This implies substantial mixing through processes such as planetary migration and the subsequent dynamical processes.

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Comments (9)

It is always going to be energetically expensive to get mass off the earth, but much cheaper energetically to get it off the moon. If we use remote robotic mining and manufacturing techniques on the far side of the moon then use linear motors to accelerate back into earth orbit, then serious manufacturing is relatively easy, and without any easily detectable effects from here on earth.

We certainly have a need to get a lot of engineering capacity out in space, and a lot of observational and interception capacity widely spread throughout the solar system, and even out further, to look for interstellar objects (rarer still, but far more energetic).

All this could be done relatively quickly, within 20 years, if we decided to devote some serious resources to it. None of it makes any sense within the economic mindset, and it makes a lot of sense if one is looking at the long term interests of humanity as a whole.

Markets are great tools for distributing scarce resources, but useless for dealing with the sort of abundance that can be created with serious robotic manufacturing.

We are on the same wavelength, tedhowardnz. I’ve been talking about mining the moon with robots and building bases and railguns for some time. With all that robots can do on the moon and with asteroids, it will be cheap to send robotic ships out to Mars and all the other moons and asteroids in the Solar System.

Robots can build large bases, all shielded from radiation, at the same time that they are working on large ships with heavy shielding to take crews to Mars and anywhere else they want to explore.

Once robots are doing all of the mining and manufacturing in orbit and on the moon, the only heavy lifting need be done into low Earth orbit, and only people need be brought up.

Robots can grow crops and raise chickens on the moon and send down shuttles to lift people up out of low Earth orbit.

Oh, one last thing I forgot to mention…when robots are printing out everything, including themselves and more printers and solar cells, then markets will find low sales for anything except plans to program into the robots for the printers, and the raw feedstock to dump into the hoppers of the printers.

But in time there will be trashgrinders for the printers, so there will be so much recycling, that the cost of feedstock will drop.

Robots will even be mining old landfills for the heavy metals that were buried there back before there was recycling.

The early adapters will send their robots out between three and four in the morning before trash pickups to carry back anything useful out of their neighbors cans and bins.

While this information on the population of asteroids is important, I prefer to wrap myself in the warm blanket of geological time and encourage science to concentrate on significantly more immediate issues facing humanity.

On a related topic, I believe the “vacuum cleaner” effect of Jupiter is one that has not been appropriately reported in the search for earth-like exo-planets. Of all the elements conspiring against the formation of life, a constant bombardment of space junk has certainly got to be high on the list. Earth, with good buddy Jupiter sweeping the solar system reasonably clean, has enjoyed the relative serenity of billions of years. On the other hand, the fortuitous arrival of the putative “dinosaur eraser”, sixty million years ago, happened at a very good time for our ancestral mammal forebears.

The timing of asteroid activity in our solar system, while following a likely common pattern early on, would not even be known, were it not for the Dino-killer.

For life like ours to exist, the many, many inevitable “bad” asteroids, must likely be followed by an appropriately timed “good” asteroid.

Well…it looks like the Solar System has been stable at least as long as people have been making observations…but that may only be for the past few thousand years.

But we are here now, so maybe things have been stable since we started to evolve from one Australopithecine or another.

Maybe, in fact, the system has been stable since that last extinction event.

So if things can just stay stable until the time comes when those asteroid miners get their robotic ships out there to meet up with carbonaceous and metallic asteroids, then we’re all in like Flynn…or at least those people at Planetary Resources will be.

But once they bring a few of those carbonaceous and metallic asteroids together and get busy mining and refining the materials they need to start printing up and assembling more mining ships and robots and finally send rare metals back to Earth, then that will be a part of the start of the coming age of abundance.